1. Field of the invention
The invention relates to a method of manufacturing assemblies composed of two bonded parts and which includes a forming phase,
2. Summary of the prior art
The method generally used up to now consists of separately hot-forming the two parts which make up the assembly under deformation conditions known as superplastic, in which great elongation is possible. The two parts are then bonded together by interposing a layer of epoxide between their surfaces which come into contact, and then placing them in an autoclave chamber in which pressure is applied in order to compress the parts together at sufficient temperature to transform the layer of epoxide into an adhesive.
Apart from the inconvenience of having to use successive pieces of equipment, this method is also disadvantageous when the assembly is a panel stiffened by hollow ribs produced by deforming one of the parts, since the pressure necessary for bonding tends to crush the ribs. To avoid this the rib cavities have to be filled manually with an crush-resistant material, such as a honeycomb structure.
Another technique for joining two parts by compression avoids the use of an adhesive by relying on the compression to cause diffusion of the material at the mating surfaces of the assembled parts. Reference may be made to French patents 2 304 438 and 2 552 500 for a description of these techniques. In all the examples known to applicants, assembly precedes the forming of the whole and, furthermore, diffusion welding is not applicable to the aluminium alloys which are an important application of the present invention.
Finally, French patent 2 374 109 describes the pressing of a coating on an airplane wing by means of balloons filled with air in order to give it the required shape, followed by demounting and the application of an adhesive layer, after which the assembly can be carried out. This process requires numerous manual operations and, generally, the interposition of an intermediate layer at the time of shaping in order to avoid any adhesion and to give the correct shape. It is designed for large parts in relatively small numbers.